Another idea is that Greninja gets exposed to some kind of meta - human - creating substance in the DC universe and gains new powers. It could then join the Teen Titans, sharing its unique Pokémon abilities with the group. It would be interesting to see how Greninja interacts with characters like Robin, Starfire, and Cyborg, and how it uses its powers in battles against the Titans' enemies.
One idea could be that Greninja, being a ninja - like Pokémon, somehow gets transported to the Naruto universe. It could team up with Naruto and use its water - based attacks in combination with Naruto's Rasengan. Maybe Greninja's ability to blend into the shadows could be used in stealth missions in the Hidden Leaf Village.
There could be unfinished business between them. They might have a shared goal that they haven't achieved yet. Greninja's return to Ash in the fanfiction could be to finally complete that goal, whether it's winning a particular Pokemon tournament or saving a certain place from destruction.
Once upon a time, Greninja was in a deep, dark forest. It was on a quest to find a special crystal that was said to enhance its water - based attacks. As it leaped from tree to tree, it sensed a strange presence. Suddenly, a group of wild Pokémon emerged. Greninja readied itself for battle, its eyes gleaming with determination.
In this fanfiction, Greninja could meet Misty. She's often associated with Pallet Town and she has her own set of water - type Pokemon. Their meeting could be interesting as Greninja is also a water - type Pokemon. They might exchange stories about their battles and experiences with water - type Pokemon.
One great 'Naruto Greninja' fanfiction is 'The Bond of Greninja'. It really delves into the unique relationship between Naruto and Greninja. The story shows how they train together and face challenges side by side, with vivid descriptions of their battles and the growth of their bond.
Writers can start by giving Greninja a clear goal, like mastering a new move. Then, they can put obstacles in its way, such as tough opponents. Also, showing Greninja's growth in its relationship with Ash can be part of the arc.
A simple fanfiction could be that Greninja and Delphox are forced to be allies when their trainers are kidnapped by an evil organization. They have to put aside their differences and work together to rescue their trainers. Greninja uses its agility to scout the enemy base, while Delphox uses its fire attacks to create distractions.
I'm not a big fan of yaoi fanfiction in general, but in the case of Greninja and Ash, it often involves a creative exploration of their relationship in a non - canonical way. Some of these fanfictions might focus on their strong bond and translate it into a more romantic or emotional connection that goes beyond friendship as seen in the original Pokemon series.
One great idea for a fanfiction could be a story where Greninja and Delphox team up to face a powerful, mysterious new Pokemon that threatens their region. They have to combine their unique skills, Greninja's speed and water - based attacks with Delphox's fire - magic and psychic abilities.